As complex designs increase, the need for rapid prototype fabrication has increased. The need for immediate fabrication of these objects require model or machine shops to fabricate complex parts quickly and to fabricate a low volume of these objects with minimum setup and run time. Most fabrication methods, however are slow, complex and expensive.
While manual machining and forming methods for these methods are often cheap and effective for simple designs, the cost can be prohibited for numerous iterations required of complex parts and assemblies. Computer numerically control (CNC) machines are widely used to automate complex fabrication, but these CNC machines are costly to operate, maintain and program just for as one of a kind production.
One lithographic fabrication method is selective laser sintering. This method employs a heat laser to fuse (sinter) selected areas of powdered material such as wax, plastic or metal. In practice, a vat of powder is scanned by the laser, melting individual particles which then stick to adjacent particles. Layers of the fused powder are processed sequentially like photopolymer lithography. An advantage of the sintering method is that a non-heated powder serves as a support for the part as it is formed. This means that the non-heated powder can be shaken or dusted off the object.
Selective laser sintering however is also a complex, expensive optical system. The resolution of the final part is limited by the beam diameter which is typically 0.01 inches to -0.02 inches. Furthermore, an additional step may be required, in that the powder is deposited and leveled by a rolling brush which requires other electromechanical components. Unfortunately, leveling fine powders with a rolling brush often causes non-homogeneous packing densities. Additionally, white powder costs less (material and labor) than liquid photopolymer, and preparing a 30 micron layer is difficult. An object built from this powder is of minimum resolution and has a non-uniform surface and often a non-homogeneous structure.
The casting industry has long used heat-disposable patterns in the making of metal objects. The process of investment casting is historically known as the "lost wax" process. This process is performed by supplying a wax pattern of the item to be cast. A geometric cavity results after the pattern is encapsulated in ceramic and is then removed by melting of the wax of the pattern. The cavity is filled with metal or other casting material which then takes the exact shape of the original pattern. Other pattern materials have been tried such as wood, foam and plastic, but these types of pattern materials are more difficult to be removed by heating. A requirement of any casting method is that the ceramic encapsulate or mold remains intact without cracking during the pattern melt or burnout.
Research has been conducted at the Massachusetts Institute of Technology in fabrication by 3-dimensional printing. In this research, ceramic powder is deposited using a wide feeder over a vat or tray. A silica binder is printed on select areas of the powder to form a solid cross-section. The process is repeated to form a stack of cross-sections representing the final objects.
This approach exhibits the same powder deposition problems as selective laser sintering along with the additional difficulty in removing unbound powder form internal cavities. Furthermore, objects generated by this system are not recyclable. The MIT research is directed toward production of ceramic molds. Metal or other materials are then injected or poured into the mold which is later broken away from the cast part. Unfortunately, the mold's internal cavities which define the final parts are not easily inspected, which leads to an expensive trial and error process to acquire accurate parts.
Rapid Prototyping or Solid Imaging systems have been introduced which form parts and models of plastic, paper, or ceramic, while under process and spatial control by computer. These models are intended to be accurate reproductions of computer data or electronic images. Such images are collected from a variety of input devices including CAD, CT scans, MRI, PET, Satellite Ranging and Imaging, Ultrasound, and Scanning Electron Microscopy.
Solid Imaging mechanisms are determined by the material candidates and lamination techniques. Most common approaches employ a laser beam to polymerize, cut-out, or otherwise sinter a vertical sequence of thin, horizontal cross-sections defining a 3-Dimensional object. These systems are costly, environmentally harmful, and often inaccurate due to thermally induced warpage. Most systems are not compatible with a typical office work area, due to resins, solvents, fumes and high power lasers.
More practical systems are based on jet or syringe type dispensers, which jet melted waxes, plastics, or alloys in sequential cross-sections which solidify on contact with the previous layer. While these systems are lower in cost and complexity than laser based systems, they suffer from lamination problems and inaccuracy, again, due to thermal stress and the difficulty in controlling the layer-to-layer bond mechanism.
Hot wax inkjets and nozzles are difficult to position quickly and precisely, especially while connected to fluid containers and electro-mechanical devices. The maintenance of temperature control, alignment and media filtration are critical to functionality for such dispensers. Bulk fluid transport is dependent on precise maintenance of fluid level, temperature, and pressure throughout the feed path, so it is desirable to keep the raw material in solid form until jetting or liquid dispensing which may be difficult.
As each layer is constructed, solid imaging systems typically generate a temporary support structure, casing, or scaffolding, which is removed after the vertical layering build is completed. Supports are generally removed manually, but automation is possible through the use of a soluble support surrounding an insoluble model.
While the soluble support is desirable, accurate placement of the two fluid materials within a layer is difficult to accomplish without overlapping of the two fluid materials. In practice, surface leveling devices are used in most systems to control the height and flatness of each layer formed. This causes excess material displacement or removal, which in turn requires a reclamation mechanism.
A laser printer includes a rotating mirror to reflect a pulsed laser beam. The laser beam is swept across a photosensitive drum to selectively charge individual pixels. These produce alternating charged and uncharged areas. The charged areas attract toner which has been positioned close by to "write black" while the uncharged area do not attract toner to "write white". The charged areas now are toner areas while the uncharged area remains free of toner. A sheet of paper may be positioned against the drum the toner areas transfer from the drum to the paper. The paper including the toner is then heated to fire the toner on the paper.
The fundamental problem is the inability to laminate thin layers composed of solid materials of opposite solubility, with common applicators, while maintaining dimensional accuracy of the laminate. The resulting 3-Dimensional laminate is required for casting patterns, color visual models, and integrated conductive pathways.